The detection of nitro-containing organic compounds is necessary for finding unexploded ordnance or buried land mines or for finding the presence of explosive materials, e.g., hidden within airline luggage. Safety or security concerns over such explosive materials require improved monitoring and/or, analysis for the detection of selected volatile nitro-containing compounds generally present as minor contaminants within common explosive compounds such as trinitrotoluene (TNT). While analytical techniques are available to detect the presence of many substances down to levels as low as parts per billion (ppb) or less, such analytical techniques generally require collecting a sample in the field, taking the sample to a laboratory, and analyzing the sample by, e.g., gas chromatography or mass spectroscopy. Such analysis requires sophisticated equipment that generally requires up to several days to obtain final results and such analysis is not generally suited to field use. Thus, present analytical techniques fail to provide any real-time information about the presence of nitro-containing organic compounds.
Another category of materials sought to be detected on a real-time basis are chemical compounds used in chemical warfare generally referred to as chemical warfare agents (CW agents) such as nerve gas or blister agents. The detection of CW agents to allow for protection of personnel or to allow for detection of suspected production sites is important.
Much prior research has been directed to developing chemical sensors that can give more rapid feedback information. One example is U.S. Pat. No. 5,151,110 wherein a sensor includes a piezoelectric substrate, preferably contained within a surface acoustic wave (SAW) device or a quartz crystal microbalance (QCM) device, and a coating, such as zeolite crystals in an inorganic silica matrix, applied to the substrate to selectively sorb chemical entities of a size less than a predetermined magnitude. While such a chemical sensor is useful, it is limited to materials that physically fit within the particular pore sizes of the zeolite crystals.
U.S. Pat. No. 4,860,573 describes a composite substrate intended for an apparatus for quantitative detection of, e.g., an organic component present in a gas or liquid. Cyclodextrin is described as one material for incorporation as an active site material into the composite substrate. However, there is no teaching or suggestion of multilayers of the active site material, nor is there any teaching or suggestion of using cyclodextrin derivatives or of forming oriented cyclodextrin derivative structures by the controlled assembly of such materials through layer by layer build up or addition.
U.S. Pat. No. 5,418,058, issued to Li et al. on May 23, 1995, describes chemical microsensors for the detection of selected organic compounds such as aromatic compounds, polyaromatic compounds, oxygen-containing organic compounds, and halogenated hydrocarbons. In the formation of the microsensor, a linking molecule of, e.g., bistrichlorosilylhexane, was used to covalently bond the sensing molecule, i.e., the cyclodextrin derivative, to the transducer surface. There is no teaching or suggestion of the detection or nitro-containing organic compounds with the disclosed chemical microsensors, nor any teaching or suggestion of asymmetrical linking agents for covalently bonding the cyclodextrin material to the transducer surface.
It is an object of the present invention to provide a chemical sensor including a cyclodextrin derivative and a method of detecting nitro-containing organic compounds and/or CW agents, preferably in an on-site, real time process.
It is a further object of the invention to provide a chemical microsensor, including a cyclodextrin derivative, having sensitivity to detect low levels of such nitro-containing chemical compounds or CW agents, preferably at a sub-ppb level.
It is a still further object of the invention to provide a reversible chemical microsensor including a cyclodextrin derivative.
Yet another object of the present invention is to provide a chemical microsensor formed through a layer by layer build up process.
Another object of the present invention is to provide a chemical microsensor formed through a layer by layer build up process using an asymmetrical bifunctional linking agent as one layer of the microsensor.
Still another object of the present invention is a chemical microsensor system utilizing a reference sensor substantially identical to a cyclodextrin-derivative containing sensor except for the cyclodextrin-derivative material layer.
Yet another object of the present invention is to form a chemical bond, i.e., a hydrogen bond between the cyclodextrin material and the target compounds.
Yet a further object of the present invention is to provide asymmetrical functionalization on the top rim of a cyclodextrin, e.g., some hydroxyl functionalization plus some methoxy functionalization, leaving at least one functionality with hydrogen bonding potential.